This invention relates to an instrument and method for optically analzing particulate samples, and, more particularly, to an instrument in which vibration is used to compact the particulate samples and eliminate any cavities or voids therein.
In U.S. Pat. No. 4,040,747 to Donald R. Webster, issued Aug. 9, 1977, there is disclosed a relatively low cost instrument for measuring and analyzing the optical properties of organic materials to determine the percentages of certain constituents of the test materials. This instrument was developed to satisfy a need for a low cost instrument to rapidly determine the moisuture, oil and protein content in produce and grain products. In the instrument disclosed in the patent, a source of wide-band infrared light is positioned to illuminate a sample of ground grain through a filter assembly in which interference filters are arranged in a wheel configuration mounted for rotation about an axis. As the filter wheel rotates, each filter is brought successively into the infrared light beam. As each filter is moved through the light beam by the filter wheel, the angle of incidence of the light beam on the filter changes and this changes the wavelength transmitted through the filter. Moreover, each filter provides a different range of wavelengths. By detecting the amount of reflection from the sample at selected specific wavelengths and the relationships of these reflectance values, the oil, protein, and water content of the sample can be accurately and quickly determined.
U.S. application Ser. No. 45,089, filed June 4, 1979 discloses an instrument similar to that disclosed in the Webster U.S. Pat. No. 4,040,747, but in which the grinding of the grain is carried out automatically in the instrument at the time the measurement is made. When the instrument is started, the grain introduced into a hopper at the top of the instrument is ground and directed into a chute, the bottom of which is arranged to receive infrared light passing through the filter wheel. The bottom of the chute is enclosed by an impeller which removes grain from the chute. As the impeller moves the grain from the chute, the grain in the chute moves through the infrared beam received by the filter wheel to provide an automatic averaging from the sample being analyzed.
The instrument disclosed in application Ser. No. 236,580 is similar to that in U.S. Ser. No. 45,089, but in which the impeller at the bottom of the chute is replaced by a vibrating trough positioned at the bottom of the chute. The vibrating trough acts as a conveyor to move the analyzed grain away from the chute. When the vibrator is off, the trough serves as a gate to stop the flow of grain. The vibrating trough also serves as an agitator by sending vibrations through the grain in the trough and up through the column of the grain positioned in the chute thereby preventing any clogging of the grain in the chute.
In the instruments as described in the above identified patent and pending applications, the grain sample is preferably ground in order to give the most precise measurement of the constituents of the grain sample. In some applications in which such precision is not necessary, it has been proposed to optically analyze the grain without grinding. When the grain is not ground, the best way to optically analyze the grain is to measure the transmittance of the grain instead of the reflectance. As in the instruments of the above mentioned patent and applications, the grain sample is irradiated with narrow band infrared light by means of a filter wheel. A photodetector is positioned to receive the light transmitted to the sample. From the light transmitted through the sample as detected by the photocell, a determination can be made as to the constituents of the grain sample.